How to make an extension that will send information that appears on one site to another site?

Question

JavaScript

You need to make an extension that will:
1. Search a specific site for the installed phrase
2. Send it to another site
3. The site will display this phrase
I'm having difficulty with:
1. How to make the extension search and read?
2. How to make the extension send?
3. How to make the second site accept and display?
I understand that the question may not be very correct.
Perhaps someone has seen an application that performs one of the necessary functions and can share the necessary part of the code, I will already convert it to what I need.
UPD: who can do this? I need a connection from one site to another (the second site is mine), through a socket through an extension (probably)

Answer 1

your second site? sockets are
not your help - make an xmlhttp request by setinterval and parse the page

Answer 2

Generally a strange task.
Why is it impossible to get the necessary data from your site right away.
It's easier and faster.
Do you need an intermediary browser extension?